Piston-type accumulators



u y 17 1956 B. N. ASHTON ETAL' 2,754 8 7 PISTON-TYPE ACCUMULATORS FiledJuly 20, 1951 INVENTORS. BENJAMIN N ASHTON JOHN P. FRAIN BY Gin-VialTHEIR ATTORNEYS.

United States Patent PISTON-TYPE ACCUMULATORS Benjamin N; Ashton andJohn P; Frain, Kingston, N. Y., assignors to Electrol Incorporated,Kingston, N Y., a corporation of Delaware Application July 20, 1951,Serial No. 237,796

6 Claims. (Cl. 138-31) This invention relates to improvements in pistontype accumulators and it relates particularly to an improved type ofpiston and sealing construction for such accumulators to prevent theescape and mixing of gas and liquid on opposite sides of the piston ofthe accumulator.

it has been found that in hydraulic accumulators, shock absorbers andthe like having a piston interposed between the gas pressure reservoirand the liquid reservoir, it is diflicult to prevent leakage of the gasand the liquid past the rings on the piston. As a consequence, the gasand the liquid tend to mingle in the narrow Zone around thecircumference of the piston between the rings and as the pressurefluctuates this mixture of liquid and gas will escape past the ringswith the result that the gas escapes into the liquid-receiving chamberand liquid escapes into the gas-receiving chamber. As the liquid leaksinto the gas-receiving chamber, the capacity of the accumulatordecreases. The escape of the gas into the hydraulic system is moreserious for the presence of air or other gas has a tendency to changethe characteristics of the system because of the compressibility of thegas.

The present invention overcomes the disadvantages of the prior pistontype accumulators and the like by modifying the accumulator piston toinclude a reservoir and a differential pressure piston which introducesliquid into the zone between the rings of the accumulator piston andbetween the piston and the cylinder wall at a higher pressure than thepressure of either the gas or liquid in the accumulator. The higherpressure between the rings prevents the gas and the hydraulic fluid fromleaking past the piston rings.

The differential piston includes a larger piston which is subjecteddirectly to the pressure of the hydraulic fluid in the accumulator andacts upon a smaller piston to force liquid received in a reservoir inthe accumulator piston out through suitable ports into a groove aroundthe periphery of the accumulator piston between the sealing or pistonrings thereon. By regulating the ratio of the areas of the pistonportions of the differential piston, it is possible to produce a verysubstantially higher liquid pressure between the piston rings than thegas and the liquid pressures on the outer sides of the piston rings,thereby precluding escape of the gas into the hydraulic system.

For a better understanding of the present invention, reference may behad to the accompanying drawing in which:

Fig. 1 is a view in longitudinal section through a typical accumulatorembodying the present invention; and

Fig. 2 is a view in section taken on line 22 of Fig. 1.

A typical accumulator, embodying the present invention, as illustratedin Figs. 1 and 2, may include a closed cylinder 10 having an air checkvalve 11 at one end thereof to permit air or other gas to be introducedunder high pressure into the chamber 12 to the left of the accumulatorpiston 13. The hydraulic fluid from the hydraulic system (not shown)enters the chamber 14 to 2,754,847 Patented July 17, 1956 the right ofthe piston 13 through a suitable pipe and coupling 15. The piston 13 isgenerally cylindrical in shape and is provided with piston ring grooves16 and 17 near its opposite ends. Mounted within the grooves 16 and 17are piston rings 18 and 19 which may be of the 0 ring type formed ofrubber or synthetic rubber. These rings are capable of movementlengthwise of the grooves, between the wiper rings 20 and 21 in eachgroove which may be formed of steel or other metal and are in tightwiping and sealing engagement with the internal wall of the accumulator10.

Even though the rings 18, 19, 20 and 21 afford a very tight seal,nevertheless after a period of operation some liquid may escape from thechamber 14 past the rings 19, 2t) and 21 and some gas may escape pastthe rings 1%, 20 and 21 toward the center line of the piston where theycan mix and flow from one chamber to the other.

In accordance with the present invention escape of liquid and gas andmixing of the gas and liquid is prevented by providing the piston 13with a differential piston 23 having a piston section 24 joined by anintegral connecting rod 25 to a smaller piston section 26. The pistonsections 24 and 25 are received in connected recesses 27 and 28 ofcorresponding size extending inwardly from the right-hand end of thepiston 13. The space between the face of the piston portion 26 and theleft-hand end of the piston forms a reservoir 29 to receive liquid. Thereservoir 29 is connected by means of one or more passages 30 to agroove 31 which extends around the periphery of the piston 13 betweenthe ring grooves 16 and 17. p

The right-hand face of the piston section 24 is exposed directly to thepressure of the liquid in the reservoir or chamber 14 so that thediiferential piston 23, as a whole, is normally urged toward the left asviewed in Fig. 1. Inasmuch as the exposed surface of the piston section24 is larger than the eifective surface area of the piston section 26,the liquid in the reservoir 29 is subjected to a higher pressure persquare inch than the pressure of the liquid in the chamber 14.Accordingly, any tendency of the liquid in the chamber 14 or the gas inthe chamber 12, the pressures of which are balanced or equal, to flowinwardly past the rings 18, 19, 2t} and 21 is opposed by the higherpressure of the liquid in the groove 31 and between the rings 18, 19,2t} and 21 so that while liquid may leak from the groove 31 into the airchamber 12 and into the liquid chamber 14, the gas from the chamber 12cannot flow into the chamber 14 and liquid from the chamber 14 cannotflow into the chamber 12.

The differential piston may be retained in the recesses 27 and 28 in anysuitable way, for example, such as by means of a snap ring 32 releasablyreceived in a groove 33 in the piston 13 in the outer end of the recess27.

The piston sections 24 and 26 are also provided with suitable sealingrings 34 and 35 to reduce leakage of the liquid from the chamber 14 andthe chamber 29 into the interior of the piston 13. However, if leakagedoes occur, the space between the piston sections 24 and 26 issufficient to accommodate a substantial amount of liquid withoutimmobilizing the dilferential piston 23. Moreover, an undesirableincrease of pressure of the air trapped in the space which mightresultin escape of air into the system cannot occur.

From the preceding description, it will be apparent that the pistonstructure of the accumulator disclosed herein prevents mixing of the gasand the liquid in the accumulator, and prevents the escape of the gasinto the hydraulic system thereby overcoming the principal disadvantageof the prior types of piston type accumulators.

It will be understood that the accumulator is susceptible tomodification and that its size and design may be modified and that theratios of surface areas at opposite ends of the differential piston maybe related in accordance with requirements. Therefore, the form ofaccumulator disclosed herein should be considered as illustrative andnot as limiting the scope of the following claims.

We claim:

1. An accumulator for hydraulic systems and the like comprising a hollowcontainer having a hollow cylinder between its ends, a piston slidableaxially in said cylinder and dividing said container into a gasreceiving chamber and a liquid receiving chamber, piston rings on saidpiston in spaced relation, said piston having a recess extendinginwardly from the end adjacent to said liquid receiving chamber, saidrecess having an inner cylinder portion with a closed end to receive afluid and an outer larger diameter cylinder portion having an open outerend communicating with said liquid receiving chamber, a piston memberhaving a small diameter piston portion at its inner end, a largerdiameter piston portion at its outer end, and a rod portion interposedbetween and fixedly connected to said inner and outer piston portionsand forming therewith an annular space between said piston portions,said smaller and larger diameter piston portions fitting slidably insaid inner and outer cylinder portions, respectively, and said annularspace forming a receptacle for receiving liquid leaking from said systemand preventing unwanted increase in the pressure of gas trapped in saidspace, and a passage from said inner cylinder portion to the exterior ofsaid piston between its ends to conduct fluid from said inner cylinderportion to the exterior of said piston between said rings and maintaintherebetween a pressure higher than the gas and liquid pressures in saidchambers.

2. An accumulator for hydraulic systems and the like comprising a hollowcylindrical container, a piston in said container dividing saidcontainer into a gas-receiving chamber and a liquid-receiving chamber,said chambers receiving gas and liquid under pressure, respectively,said piston being movable freely along said container to vary thecapacities of said chambers, sealing rings encircling said piston inspaced-apart relation to form a seal between the piston and the innerwall of the container, a recess extending into said piston from the endadjacent to said liquid-receiving chamber, said recess having an innercylindrical portion having a closed inner end and an outer cylindricalportion of larger diameter than said inner portion, a passage in saidpiston leading from the inner end of said recess to the periphery ofsaid piston between said sealing rings, and another piston mounted insaid recess for axial movement therein, said another piston having asmaller diameter inner portion fitting the inner cylindrical portion ofsaid recess and forming therewith a reservoir for receiving fluid, saidanother piston having a larger diameter portion slidable in said outercylindrical portion and having its end directly exposed to pressure insaid liquid-receiving chamber.

3. An accumulator for hydraulic systems and the like comprising a hollowcontainer having a tubular portion between its ends, a first pistonslidable in said tubular portion and having sealing rings adjacent toits opposite ends engaging the tubular portion, said first pistondividing said container into separate chambers, said chambers beingadapted to receive fluids under pressure, said first piston having arecess extending inwardly from one end, said recess being adapted toreceive a fluid, a second piston mounted in said recess for axialsliding movement relative to the first piston to exert pressure on fluidin said recess and to relieve said fluid of pressure, said second pistonhaving an outer end portion exposed to the pressure of the fluid in thechamber adjacent thereto and movable thereby relative to the firstpiston, said second piston having an inner end portion of smallercross-sectional area than the outer end portion fitting in said recess,and a passage through which fluid in said recess can be forced by saidsecond piston extending from the inner end of said recess to theperiphery of said first piston between said rings.

4. An accumulator for hydraulic systems and the like comprising a hollowcontainer having a first hollow cylinder between its ends, a firstpiston slidable axially in said first cylinder and dividing saidcontainer into a gasreceiving chamber and a liquid-receiving chamber,piston rings at opposite ends of said first piston, a second cylinder insaid first piston to receive a fluid, a second piston in said secondcylinder movable in said second cylinder in response to pressure in saidliquid-receiving chamber to apply to fluid in said second cylinder ahigher pressure than the pressure in said liquid-receiving chamber, anda passage for fluid extending from said second cylinder to the exteriorof said first piston between the rings on said first piston and firstcylinder.

5. An accumulator for hydraulic systems and the like comprising a hollowcontainer having a hollow cylinder between its ends, a piston slidableaxially in said cylinder and dividing said container into agas-receiving chamber and a liquid-receiving chamber, said piston havingspaced apart piston rings thereon engaging said hollow cylinder, saidpiston having a recess extending inwardly from the end adjacent to saidliquid-receiving chamber, said recess having an inner cylinder portionwith a closed end and an outer larger diameter cylinder portion havingan open outer end communicating with said liquid-receiving chamber, saidinner cylinder portion being adapted to receive a fluid, a piston memberhaving portions of different diameters on its inner and outer endsslidably mounted in and fitting the inner and outer cylinder portions,respectively, the outer end of said piston member being exposed directlyin said liquid-receiving chamber, and a passage extending from saidinner cylinder portion to the exterior of said piston between saidrings.

6. An accumulator for hydraulic systems comprising a hollow containerhaving a hollow cylinder between its ends, a piston slidable axially insaid cylinder and dividing said container into a gas-receiving chamberand a liquidreceiving chamber, piston rings on said piston in spacedapart relation, said piston having an expansible and contractile chambertherein to receive liquid, a passage extending from the last-mentionedchamber to the periphery of said piston between said piston rings, andmeans responsive to pressure in said liquid-receiving chamber forcontracting said expansible and contractile chamber to exert a greaterpressure between said rings than the pressure in said liquid-receivingchamber.

References Cited in the file of this patent UNITED STATES PATENTS2,349,253 Edmund May 23, 1944 2,417,256 Kremiller Mar. 11, 19472,440,065 Ashton Apr. 20, 1948

